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Disease Cycle and Epidemiology

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A) Colletotrichum cereale overwinters as mycelium or stromata associated with stolons and stems in thatch. B) In spring, infection begins on leaf sheaths and stolons. This early infection can result in symptoms of anthracnose basal rot. C) Multiple acervuli on infected turfgrass foliage produce conidia that are splashed or displaced from leaves to infect healthy turfgrass plants. Anthracnose foliar blight causes thinning of turfgrass during early to mid-summer. D) The fungus penetrates epidermal cells and colonizes mesophyll cells. Yellow foliar lesions and black acervuli develop.

Epidemiology

Anthracnose develops over a range of temperatures. Symptoms of basal rot develop at cooler temperatures (15 to 25°C, or 60 to 78°F), and foliar symptoms occur at temperatures above 26°C (79°F). Anthracnose foliar blight outbreaks have been predicted by using a combination of leaf wetness duration and temperature. Continuous leaf wetness of 12 hours or more and temperatures of 14 to 28°C (57 to 82°F) are necessary for infection, which intensifies with increasing temperature and leaf wetness duration. The latent period (the time between infection and production of new spores) is thought to be 10 to 12 days.

Juvenile plants display good resistance to foliar blight caused by C. cereale. As plants mature, initial symptoms develop on older, senescing leaves. In annual bluegrass, foliar symptoms of anthracnose increase in severity following anthesis (opening of flowers). Plants subjected to drought and/or fertility stress are believed to be more susceptible to infection.

Host specificity. Isolates of C. cereale show a degree of host specificity to either annual bluegrass or creeping bentgrass, although some isolates can infect both turfgrass hosts. DNA analysis indicates that isolates from annual bluegrass, creeping bentgrass, and corn are genetically different. Furthermore, genetic similarities among C. cereale isolates are influenced more by plant host than by geographic origin. For example, isolates of C. cereale from creeping bentgrass and annual bluegrass may differ in the length of both appressoria and spores. Results of one study indicated that mean appressorial length was approximately 0.8 µm longer for creeping bentgrass isolates than for annual bluegrass isolates. In contrast, mean spore length was 1.5 µm shorter for creeping bentgrass isolates than for annual bluegrass isolates. In addition, when cultured on agar media, the color of C. cereale colonies was influenced by turfgrass host. Black-gray cultures were isolated from creeping bentgrass, and cultures with pink coloration were isolated from annual bluegrass.

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